In a conventional cellular base station, various signal processing operations are performed on uplink and downlink cellular communication signals by distinct hardware sub-systems that may be located some physical distance away from each other. For example, FIG. 1 illustrates an example of a conventional cellular base station 100, which includes a tower 110, a plurality of antenna arrays 120, 121, 122 (or “sectors”), a plurality of remote radio units (RRUs) 130, 131, 132, and a baseband unit 140.
The plurality of antenna arrays 120-122 (e.g., each array including multiple antennas, such as four, eight, or some other number of antennas) are mounted on the tower 110 at some height above the ground. In addition, the RRUs 130-132, also commonly referred to as “radio heads,” are mounted on the tower in locations that are physically close to the antenna arrays 120-122 (e.g., also at some height above the ground). In some cases, an RRU 130-132 and an antenna array 120-122 may be integrated together within a single subsystem, and such an integrated subsystem may be referred to as an “active array.” Either way, each RRU 130-132 is communicatively coupled to one of the antenna arrays 120-122, and downlink and uplink signals are exchanged between each RRU/antenna array pair. More specifically, each RRU 130-132 provides downlink radio frequency (RF) signals to an antenna array 120-122 for transmission, by the antenna array 120-122, of corresponding wireless radio signals 123 over the air interface (e.g., to mobile devices such as cellular telephones or other cellular communication devices). In addition, each RRU 130-132 receives uplink RF signals from an antenna array 120-122, which the antenna array 120-122 produces from corresponding wireless radio signals 124 received from the mobile devices over the air interface.
The baseband unit 140 is typically located on the ground near the base of the tower 110, for example in an equipment room, sometimes further away, and potentially co-located with other baseband units. The baseband unit 140 is communicatively coupled to the plurality of RRUs 130-132 through cables 150, 151, 152. Typically, a single cable 150-152 provides connectivity between the baseband unit 140 and each RRU 130-132. Thus, in a base station that includes three RRUs (e.g., base station 100), three cables typically would provide connectivity between the baseband unit and the RRUs. The cables may be, for example, Ethernet cables, fiber optic cables or coaxial cables. In addition, in some systems, the connection between an RRU and a baseband unit alternatively may be implemented as a wireless backhaul.
In conjunction with downlink communications, the baseband unit 140 produces downlink data and communicates the downlink data to the RRUs 130-132 over the cables 150-152. In conjunction with uplink communications, the RRUs 130-132 produce uplink data and communicates the uplink data to the baseband unit 140 over the cables 150-152. Both the downlink data produced by the baseband unit 140 and the uplink data provided by the RRUs 130-132 is communicated over the cables 150-152 according to a defined standard, such as the Common Public Radio Interface (CPRI) standard, for example.
A number of wireless standards are implemented to provide cellular communications between base stations and user equipments. For example, some common wireless standards include GSM (Global System for Mobile communications), WCDMA (Wideband Code Division Multiple Access), WiMAX (Worldwide Interoperability for Microwave Access), Wi-Fi (wireless local area networking based on IEEE 802.11 standards), 4G LTE (Long Term Evolution), and more recently, 5G. Many recent standards, including WiMAX, Wi-Fi, 4G LTE, and 5G, are based on Orthogonal Frequency Division Multiplexing (OFDM), OFDMA (Orthogonal Frequency-Division Multiple Access) and SC-FDMA (Single-Carrier Frequency Division Multiple Access). Using such standards, users' data is conveyed over subcarriers. Typically, the subcarriers are defined by frequencies that are distributed around a carrier center frequency (or “carrier”), with a defined subcarrier spacing between adjacent subcarriers.
Some cellular communications protocols, such as OFDM, utilize multi-carrier modulation techniques to convey users' data through sets of subcarriers that are centered around multiple adjacent carriers. At some point along the downlink and uplink signal processing chains, the multiple signals associated with the multiple carriers must be conveyed between the baseband unit (e.g., baseband unit 140) and the RRUs (e.g., RRUs 130-132) through the cables (e.g., cables 150-152). For example, in a system in which communication is carried out using three carriers, a set of cables may include three cables (e.g., cables 150-152) to communicate between the baseband unit and three RRUs, where each cable conveys multiple downlink and uplink streams associated with the plurality of antennas in the subsequent antenna arrays (e.g., the antennas in each antenna array 120-122).
As can be imagined, the set of cables coupling the baseband unit to the RRUs is a system feature that may limit the amount of data that may be communicated between the sub-systems. Although the use of additional cables may be one way to increase data throughput, the additional cables add system cost and complexity. Accordingly, recent development has been underway to implement data compression techniques. However, the desire for ever-higher data rates continues to present challenges. Accordingly, system designers strive to develop new techniques for base station operation that may enable higher data throughput rates without adding significant system cost or complexity.